Teves III convert back to vacuum booster - questions

There are also tandem boosters that are smaller in diameter but longer- check Speedway Motors.

Good point. This measures 3 inches and 11 1/2 inches. So about 3.8 to 1.

Cool. Offhand, though, I’d like to see a design for a bolt-on clevis, something you could sell and the customer could just drill a coupla holes and bolt it on.

Of course, you’d still need a clutch pedal. It’d be nice if the dimensions were available so anyone could fab one.

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Yeah, bolt on should be doable. Maybe fab something out of steel channel. The pedal box is fairly meaty, shouldn’t be a problem to find a place to bolt it to.

Specific to what I am doing, it seems like it should be easier to modify a Teves clutch pedal box to fit vacuum brakes, vs. say modding a vac auto pedal box to take a clutch. But I’m not there yet. Still some fiddling to do with pedal heights… the brake pedal looks low compared to where the clutch pedal might end up sitting. Since I pushed the booster (and thus the actuator rod) forward 1/4", at the aforementioned 3.83:1 ratio, I have lowered the brake pedal an inch. That assumes that the “face” of the Teves box is the same distance from where the actuator connects as it is on the vac box.

And of course it still and open question of whether things will actually fit in the car. Might be able to get there tomorrow.


Just happened on this. I know nothing about it, but it looks nice…

This pivot looks bolted on…

That thing is sweeet.

Teves unit out of car and on bench reveals a problem I should have caught before now. The actuator rod is quite a bit shorter on the vac booster versus the teves unit. About an inch. There are various ways to address this, I may build a spacer, or I may explore a threaded actuator rod. To be determined. First I will test fit the new unit in the car and confirm that this booster is actually going to work. If it does not, then I can look for alternatives that are not only smaller diameter, but have an adjustable actuator rod.

That’s a Teves III unit? Somehow I thought they were longer.

Well, now we have lots of fun problems. Number one, the booster does not clear the fender well. It’s hitting right where the blue tape is. Pedal box is about a half inch from sitting down flush onto the firewall.
Number two, that booster angle doesn’t look right at all to me. It might get a little bit better if I can get it to sit flush on the firewall, but I don’t think it’s gonna make enough of a difference. The “vertical” face on the Teves box is not actually vertical, maybe the one on the stock vacuum box is more so.
Number three, I’m starting to think that I have pedals for a right hand drive car. The pedal box casting number is the same for left and right hand drive car but the pedals them selves are not. This brake pedal, yes that’s the brake pedal, is way off. The only part number on my petals that makes any sense at all is CAC 5613. Which is on the clutch pad. And, the parts manual I have, shows CAC 5613, and CAC 5612, as clutch pedals. It does not say which is left and which is right hand drive. UPDATE: 5613 is a RHD pedal. sigh.

That’s easy: a little polishing with a #4 ball pein hammer, and she’ll fit.


In the pic above of the Teves unit, does the joint around the edge of the plastic reservoir sit level in the car? Indicating that the master cylinder does NOT sit level, it points nose-up? Because I think the pre-ABS master cylinder and vacuum booster sits pretty close to level. That would seem to indicate that the mounting face on the ABS pedal housing is at a different angle than the one on the pre-ABS. And perhaps a different height as well.

You might be able to fix all this with a revised adapter plate, one that’s wedge-shaped this time. But again, I think it’d be easier to get a pre-ABS brake pedal housing and fab a bracket to hold a clutch pedal.

It does sit level at the joint, and I have been thinking the same thing. Next step is to fit the housing w/o the booster attached and see how much slope there is when it’s seated properly.
Regarding the RH pedal problem,
I can use the stock auto box brake pedal, possibly cutting down the pad. The RHD clutch pedal needs to be made straight so that it doesn’t sweep left, I can do that with a torch.
Regarding the mc clearance, Summit makes a 7” booster that will bolt up (jag one is 9”) so that’s solvable. It includes a threaded actuator rod which solves
the pedal height problem.
All moot if the angles are wrong, so gotta check that next.

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Are those dimensions depth or diameter? If diameter, does a smaller diameter mean less boost?

That dimension is diameter. Yes, smaller means less boost, which means a heavier pedal. I don’t mind it a bit heavier, if I go this route we’ll have to see if it’s too heavy. Another alternative is a dual-diaphragm 7", which gives more boost than same diameter single-diaphragm. However, they are quite a bit thicker, which means it may hit the fender well in the same spot. Here’s some real data:

Note that these numbers don’t really align with the XJS in terms of pedal ratio, vacuum, etc., but they are good for comparison.

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Hi Greg-
Hoping I can impose for another pic…
Can you take one from the passenger side looking across to the vac booster, with the camera low, like on the fender? I want to see how much “tilt” there is in the vac booster.

Also, what is the clearance between the MC and that cross brace? An inch? More?

thank you!

Well, the tilt on the pedal box was not as severe as I feared. In the below pics the bottom of the straight edge is the centerline. The long ruler is vertical and you can see the tilt on the face of the adapter plate.

In other news, the jag booster is too large in diameter. The centerline on a non-abs pedal box must be a bit higher.
The good news is that I am pretty sure the summit booster will work. I think the mc will clear the cross brace, there’s about 2” from the centerline of the mc to the bottom of the brace

Since I am giving up some boost I will explore smaller bore-diameter mc. Stock is 15/16. I think Wilwood makes some remote reservoir options. Since my pedal height with the booster is easily adjustable, the extra travel should not be a big deal.

The distance between cross brace and front plastic elbow is 3/4".

Not sure this is the photo you requested?

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That works, thank you!

I’m going to ask if you have checked two other possibilities. First, I’m wondering if it would fit as-is except that you’re trying to rock it in, and it won’t rock, it must be dropped straight down. And possibly your screwy pedals preventing it from being manipulated correctly.

The other possibility is that your cobbled brake pedal housing is trying to hold the booster too far forward. Obviously, it must be located correctly axially to fit into that recess in the fenderwell. A bit too far forward would cause it to make contact precisely where you say it’s making contact.

One other question: Besides the 9" and the 7", apparently there’s also an 8"? Why aren’t you considering that?

Also: The booster you have – is that the correct part for the pre-ABS XJ-S?

Y’know, if you could get ahold of a pre-ABS brake pedal housing, you could slap that booster on it and see if it fits into the car. Then you could decide if you can get there with the housing you have or to fab a clutch pedal pedestal to attach to the pre-ABS housing.

If you got it from a junkyard, you could also get a brake pedal with it. The A/T pedal itself is too wide for manual transmission use, but it’s a cinch to cut down.